The system of this application is designed to control the attitude of a satellite. Satellites must be maintained in a predetermined orbit and attitude in order to accomplish the assigned mission which can be surveillance, photography, detection and many others. The orbit and attitude of the satellite must be periodically adjusted to compensate for disturbances which occur in space or for the purpose of changing the mission.
In general, spacecraft attitude is adjusted by activating actuators, such as, momentum wheels, magnetic torguers, or thrusters in response to an attitude correction signal. The attitude error may be sensed by reference to sensors monitoring the position of the sun, stars and earth relative to the satellite or by onboard inertial sensors such as gyroscopes. The attitude is adjusted to its mission orientation in which the system is pointed at its predetermined target and is maintained in this orientation during orbital flight. During flight the satellite is subject to motions induced by external forces, on board mechanisms or other sources and the attitude control system must continuously monitor and adjust attitude. Attitude control is therefore of primary importance in order to point the satellite to accomplish its mission and to maintain that position with the required accuracy.
It is a purpose of this invention to use fuel efficient reaction wheels to achieve attitude corrections wherever possible. This is accomplished while obtaining a tighter pointing capability with increased spacecraft autonomy. It is a purpose of this invention to utilize four reaction wheels preferably arranged in a trihedral configuration to provide better performance and enhanced redundancy.